We shall pursue the following objectives: 1. Add to our collection of 52 pseudorabies (Pr) virus ts mutants, virus mutants isolated after mutagenesis of specific regions of the genome. We shall construct a complete genetic and physical map of the Pr virus genome. 2. Study in detail the interactions of viral DNA molecules within the infected cells in an attempt to gain an understanding of the processes leading to the two isomeric orientations of the short unique region of the genome. 3. Study the pathways leading to the cleavage of the concatemeric viral DNA and the assembly of the viral nucleocapsids using ts mutants defective in these functions. 4. Study the transcription and processing of immediate-early (IE) RNA. The nature of the IE proteins and their functions in terms of binding to specific regions of the genome or modifying the activity of the cellular DNA-dependent RNA polymerase II will also be studied.